Doppler-nulling traveling-wave antenna relays for high-speed vehicular communications

ABSTRACT

An antenna relay system for facilitating wireless communication between mobile terminals on a high-speed rail vehicle and stationary base stations with substantially reduced Doppler shift effects comprises matched traveling wave directional antennas mounted to a high-speed rail vehicle and positioned collinearly alongside the railway. Both antennas continually transmit and receive at a fixed angle relative to the motion of the train so as to circumvent the Doppler shift. The signal transmitted or received by the stationary antenna is conducted to a nearest node for communication with an access network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation under 35 U.S.C §120 of U.S. patentapplication Ser. No. 13/395,880 filed on Mar. 13, 2012, now U.S. Pat No.8,948,690, which is the National Stage filing under 35 U.S.C §371 of PCTApplication Ser. No. PCT/US 11/52575 filed on Sep. 21, 2011.

The disclosures of the U.S. Patent Application and PCT Application areherein incorporated by reference in their entireties.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Advanced wireless communication systems achieve greater bandwidthefficiency by partitioning the communication channels into increasinglynarrow sub-channels. The receivers, in turn, need to use selectivefilters in order to separate the different carriers, rendering thesesystems susceptible to interference created by a frequency mismatchbetween the transmitter and receiver. A Doppler shift resulting from themotion a transmitter relative to the receiver generates a frequencyoffset that may become problematic for wireless communication withhigh-speed vehicles.

Strategies for mitigating Doppler shifts such as adjusting transmissionfrequency or using rake receivers in the frequency-domain fail tocorrect the underlying problem, the change in carrier frequencyintroduced by the relative motion of the transmitting and receivingantennas. The Doppler shift impacts wireless communication most severelyin high-speed transportation systems such as High Speed Rail (HSR). HSRcommunication systems enabling passengers to use their wirelesscommunication devices such as cellular phones typically have a fixedinfrastructure that supports wireless communication.

SUMMARY

The present disclosure generally describes techniques for enhancedwireless communication between mobile terminals on high-speed vehiclesand stationary base stations.

According to some examples, a method for enhancing wirelesscommunications in high-speed vehicles through Doppler-nullingtraveling-wave antenna relays may include aggregating wireless trafficfrom a plurality of wireless communication devices at an access terminalon a moving vehicle; and forwarding the wireless traffic to a wirelesscommunication network through a pair of matched traveling-wavedirectional antennas. A first of the antennas may be positioned on themoving vehicle and a second of the antennas may be positioned along apath of the moving vehicle. The second antenna may be conductivelycoupled to one or more access nodes of the wireless communicationnetwork.

According to other examples, a wireless communication system enablingcommunication between high-speed vehicles and a terrestrial networkthrough Doppler-nulling traveling-wave antenna relays may include anaccess terminal adapted to aggregate wireless traffic from a pluralityof wireless communication devices on a moving vehicle and forward theaggregated wireless traffic to the terrestrial network through a pair ofmatched traveling-wave directional antennas, a first traveling-wavedirectional antenna affixed to the moving vehicle, and a secondtraveling-wave directional antenna positioned along a path of the movingvehicle. The second antenna may be conductively coupled to one or moreaccess nodes of the wireless communication network.

According to further examples, a traveling-wave, directional antennasystem for enabling wireless communication between high-speed vehiclesand a terrestrial network may include a first traveling-wave directionalantenna affixed to a moving vehicle adapted to receive aggregatedwireless traffic from a plurality of wireless communication devices onthe moving vehicle and forward the wireless traffic to the terrestrialnetwork through a matching second traveling-wave antenna and the secondtraveling-wave directional antenna positioned along a path of the movingvehicle and conductively coupled to one or more access nodes of thewireless communication network.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The below described and other features of this disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several embodiments in accordance with thedisclosure and are, therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings, in which:

FIG. 1 illustrates a graph of the Doppler shift from a movingtransmitter seen by a stationary receiver;

FIG. 2 illustrates Doppler-nulling travelling-wave antenna relays inhigh-speed rail wireless communications;

FIG. 3 illustrates an example configuration of the Doppler null for apoint transmitter and receiver;

FIG. 4 illustrates an example configuration of a distributed Dopplernull for a travelling-wave transmitter and receiver:

FIG. 5 illustrates leaky coaxial cable suitable for use as atravelling-wave directional antenna in high-speed rail wirelesscommunications;

FIG. 6 illustrates an example cellular-repeater configuration, which maybe used to control cellular telephone communications through atraveling-wave directional antenna;

FIGS. 7A and 7B illustrate example point-to-point andpoint-to-multipoint client-bridge configurations, which may be used tocontrol packetized data communications through a traveling-wavedirectional antenna;

FIG. 8 illustrates a general purpose computing device, which may be usedfor software control of wireless communications through atravelling-wave directional antenna in lieu of the hardwareimplementations of FIGS. 6 and 7;

FIG. 9 is a flow diagram illustrating an example method for use oftravelling-wave directional antenna in high-speed vehicle wirelesscommunications that may be performed in a computing device such asdevice 800 in FIG. 8;

FIG. 10 is a flow diagram illustrating an example method for use oftraveling-wave directional antenna in high-speed vehicle communicationsthat may be performed in a cellular repeating device such as 620 in FIG,6;

FIG. 11 is a flow diagram illustrating an example method for use oftraveling-wave directional antenna in high-speed vehicle communicationsthat may be performed in a client bridge device such as 718 in FIG. 7;and

FIG. 12 illustrates a block diagram of an example computer programproduct, all arranged in accordance with at least some embodimentsdescribed herein.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented herein. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe Figures, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

This disclosure is generally drawn, inter alia, to methods, apparatus,systems, devices, and/or computer program products related to enhancingfor wireless communication between mobile terminals on high-speedvehicles and stationary base stations.

Briefly stated, an antenna relay system that comprises matched travelingwave directional antennas mounted to a high-speed rail vehicle andpositioned collinearly alongside the railway provides wirelesscommunication between mobile terminals on the high-speed rail vehicleand stationary base stations substantially reducing Doppler shifteffects. Both antennas may continually transmit and receive at a fixedangle relative to the motion of the train so as to preclude Dopplershift of the signals. The signal transmitted or received by thestationary antenna may be conducted to a nearest node for communicationwith an access network.

FIG. 1 illustrates a graph of Doppler shift from a moving transmitterseen by a stationary receiver. As discussed above, narrow sub-channelsare used for enhanced bandwidth efficiency in advanced wirelesscommunication systems. This results in a need for receivers withselective filters in order to separate the different carriers, renderingthese systems susceptible to interference created by a frequencymismatch between the transmitter and receiver. As illustrated in graph100, the Doppler shift 110 resulting from the motion a transmitterrelative to the receiver generates a frequency offset.

In 3GPP LTE systems, for example, the nominal Orthogonal FrequencyDivision Multiplexing (OFDM) sub-channel spacing is 15 kHz, while forscalable OFDM in mobile WiMax the sub-channel spacing can be as small as10 kHz. High-speed conventional rail lines can operate at top speeds of350 km/h, producing a Doppler shift of up to 780 Hz for a 2.4 GHzcarrier frequency. If uncorrected, frequency shifts of this magnitudecan cause inter-carrier interference that may significantly degrade thesystem performance. The situation may further be exacerbated bymultipath effects, where different signal paths not only introducedifferent time delays (producing inter-symbol interference) but thedependence of the Doppler shift on the motion of the transmitterrelative to the reflecting path may also produce different frequencyshifts for the different paths, further contributing to inter-carrierinterference.

Graph 100 illustrates, across frequency axis 104 and amplitude axis 102,inter-carrier interference 112 caused by the Doppler shift 110 betweenmoving transmitter sub-channels 108 and receiver sub-channels 114. Oneof the strategies for mitigating Doppler shifts includes a base stationinstructing the mobile transmitter to adjust its transmission frequency,although the tuning range for a mobile terminal may be limited andfrequent updates necessitated by the changing transmission angle mayincur considerable signaling overhead. Another approach includes use ofrake receivers in the frequency domain to resolve each multipath signalfrom a single mobile terminal using a different branch of the receiver.However, the potential for inter-carrier interference between mobileterminals may remain even with this strategy. Further, none of thesestrategies corrects the underlying problem, the change in carrierfrequency introduced by the relative motion of the transmitting andreceiving antennas.

HSR, which is a transportation mode highly susceptible to Doppler shifteffects on wireless communication, is also amenable to the disclosedapproach because of its fixed infrastructure. Embodiments virtuallyeliminate the Doppler shift in wireless communications with mobileterminals on high-speed rail by relaying the signals through a collineartraveling-wave antenna system mounted on the moving train and alongsidethe railway. The matched traveling wave directional antennas of a systemaccording to embodiments may continually transmit and receive at a fixedangle relative to the motion of the train so as to circumvent theDoppler shift. The signal transmitted or received by the stationaryantenna may be conducted to a nearest node for communication with anaccess network. The approach exploits the directional dependence of theDoppler spectrum of a moving transmitter by concentrating the radiosignal in a distributed highly-directional transmission at the angle ofthe Doppler null, eliminating the Doppler frequency shift. According tosome embodiments, the traveling-wave antennas may be made using leakycoaxial cable designed to radiate at the angle of the Doppler null.

FIG. 2 illustrates Doppler-nulling travelling-wave antenna relays inhigh-speed rail wireless communications in accordance with at least someembodiments described herein.

Embodiments enable wireless communication between mobile terminals onhigh-speed vehicles (particularly high-speed rail) and stationary basestations without suffering Doppler shifting of the signal frequency dueto the vehicle's motion. This capability is possible because the Dopplershift in radio transmissions from a moving transmitter depends upon theangle of the signal path relative to the direction of motion of thetransmitter. By pairing a traveling-wave directional antenna on the HSRwith a matched traveling-wave directional antenna positioned alongsidethe railway, a communication channel may be established at a continuousDoppler null—the geometric configuration in which the Doppler effectintroduces zero frequency shift on radio signals between a movingtransmitter and a stationary receiver (and vice-versa).

Traveling-wave antennas use a traveling wave on a guiding structure asthe main radiating mechanism, and when suitably designed they are ableto radiate continuously along their length in highly directional beams.Diagram 200 depicts an implementation of a Doppler-nulling antenna relaysystem for mobile wireless communication in high-speed rail, using anaerial configuration. Each train car 230, 240 may include an intra-carnetwork 262, 264 comprising wireless nodes 232, 242 (e.g., routers) andgateways 234, 244 (e.g., cellular repeaters or wireless bridges) forfacilitating communication between on-board wireless devices (e.g.,laptop 236 and cellular phone 238) and an access network. Gateway 252 intrain car 230 may be coupled to gateway 244 in train car 240 as part ofthe inter-car network 266, or the gateways may be configured to operateas independent sub-networks.

The wireless traffic may be aggregated at a main access terminal 248 onthe train and transmitted to the terrestrial access network using pairedtraveling-wave directional antennas 245 and 226 (leaky coaxial cables)mounted to the roof of the rail car and positioned along the railway,respectively; this step does not entail reprocessing of the wirelesstransmissions. Both traveling-wave antennas may continually transmit andreceive (256) at a fixed angle (254) relative to the motion of thetrain. The signal transmitted or received by the stationary antenna maybe conducted by the leaky coax positioned along the railway 226 to anearest node for communication with the access network. Because of thedirectional nature of the antenna coupling, signals received from themoving vehicle may be conducted to the node behind the vehicle (222),while signals transmitted to the moving vehicle may be conducted fromthe node in front of the vehicle (224).

FIG. 3 illustrates an example configuration of the Doppler null for apoint transmitter and receiver in accordance with at least someembodiments described herein.

When a mobile terminal moves toward a receiver the frequency of thereceived radio signal is increased (370), and when it moves away thefrequency is decreased (390)—known as Doppler shift. As the terminalpasses by the receiver, the frequency shift changes from positive tonegative, and at one point the signal is momentarily unshifted. Thispoint is known as the Doppler null.

For point transmitters and receivers, the Doppler null occurs fortransmitted signals that pass through the midpoint between transmitterand receiver at the point of closest approach 380. The transmissionoriginates before the point of closest approach, the reception occursafter the point of closest approach, and the angle of transmission 384is perpendicular to the paths of the transmitter 382 and receiver 386 ina frame in which the midpoint is stationary. This configuration isportrayed in diagram 300.

The angle of signal launch and signal reception may be obtained bytransforming to a frame where the transmitter or receiver is stationary.In the (stationary) frame of the emitter, this results when the angle θis given by:

$\begin{matrix}{\theta = {{\cos^{- 1}\left( \frac{1 - \sqrt{1 - {v^{2}/c^{2}}}}{\frac{v}{c}} \right)} \approx {\cos^{- 1}\left( \frac{v}{2\; c} \right)}}} & \lbrack 1\rbrack\end{matrix}$where θ is the transmission angle relative to the direction of motion ofthe emitter, v is the speed of the emitter, and c is the speed of light.For speeds characteristic of a terrestrial vehicle (≦400 km/h), θdeviates from 90° (broadside transmission) by no more than ˜10⁻⁵degrees.

FIG. 4 illustrates an example configuration of a distributed Dopplernull for a travelling-wave transmitter and receiver in accordance withat least some embodiments described herein.

The instantaneous geometry of FIG. 3 may be replaced by a continuousgeometry when a travelling wave emitter 406 and receiver 408 are used.As shown in diagram 400, the transmitted signal 404 is continuallyradiated and subsequently received (402) by the traveling-wave receiver408 as the transmitted signal 404 propagates up the travelling waveemitter 406. The path for the entire wave front 410 conforms to theconfiguration of a Doppler null.

Leaky coaxial cable can function as a directional traveling-wave antennaif the (periodic) spacing of the slots in the outer conductor sheathcouples the guided wave mode into a single radiation mode. Thewavenumber vector in these structures is complex as a result ofradiation loss, and the phase velocity typically exceeds the speed oflight. The lowest radiation mode that couples to a guided-wave mode isthe negative fundamental, −1 mode, for which the radiated wave front isangled backward relative to the direction of propagation of theguided-wave. The radiation angle of this −1 mode may be given by:θ⁻¹=sin⁻¹(√{square root over (ε−λ/P)})  [2]where ε is the dielectric constant of the coaxial spacer material, λ isthe free space wavelength of the radiated wave, and P is the period ofthe spacing between the slots in the coaxial cable.

One characteristic of such periodic structures is the occurrence of astop band in the guided-wave mode at wavelengths that couple into thebroadside radiation mode (θ≈90°). These are wavelengths for whichequation [2] satisfies equation [1] for a moving antenna on HSR.

FIG. 5 illustrates leaky coaxial cable 500 suitable for use as atravelling-wave directional antenna in high-speed rail wirelesscommunications in accordance with at least some embodiments describedherein.

In a practical leaky coaxial-cable design for use as a travelling-wavedirectional antenna such as leaky coaxial cable 500, the slot geometry(518) provides highly directional coupling between collinear antennapairs for the design frequencies at angles 520 close to 90°, as requiredfor Doppler nulling. Interleaving a second array of slots offset by P/4(514) from the first set separated by P (512) eliminates the stop band,permitting the use of leaky coaxial cables as traveling-wave directionalantennas suitable for Doppler nulling relay systems.

Because signals received at 90° couple equally into forward and backwardpropagating modes, it is further advantageous to design the directionalantennas to transmit and receive at a small angular offset from 90° soas to separate the direction of conduction of the transmitted andreceived signals in the traveling wave antennas. The resulting frequencyshift in the communicating signal can be kept small enough to notintroduce intercarrier interference. The Doppler shift resulting fromdirectional antennas transmitting at an angle that deviates from 90° byan amount φ is given by:

$\begin{matrix}{{\Delta\; v} = {v\frac{v}{c}\sin\;\phi}} & \lbrack 3\rbrack\end{matrix}$For example, the Doppler shift accruing to a 2.4 GHz signal relayedto/from a train traveling at 350 km/hr using directional antennas thattransmit at angles from 5° to 10° lies in the range of 25 Hz to 135 Hz,respectively.

While embodiments have been discussed above using specific examples,components, scenarios, and configurations in FIG. 2 through FIG. 5, theyare intended to provide a Doppler-nulling traveling-wave antenna relayfor high-speed vehicular communications. These examples do notconstitute a limitation on the embodiments, which may be implementedusing other components, frame selection schemes, and configurationsusing the principles described herein.

FIG. 6 illustrates an example cellular-repeater configuration in diagram600, which may be used to mediate cell phone communications through atraveling-wave directional antenna 614 in accordance with at least someembodiments described herein. In a basic configuration, a cellularrepeater 620 includes an internal reception antenna 622, an internalbroadcast antenna 624, and a bidirectional signal amplifier 626 that isconnected (628) to the traveling wave directional antenna 614 mounted tothe rail car 612. While antennas 622 and 624 are illustrated as twodifferent types of antennas, they may be any type of suitable antenna ofthe same type or of different types.

FIGS. 7A and 7B illustrate example point-to-point andpoint-to-multipoint client-bridge configurations, which may be used tocontrol packetized data communications through a traveling-wavedirectional antenna in accordance with at least some embodimentsdescribed herein. In a basic configuration, a wireless bridge(point-to-multipoint router 718 or combination of point-to-point bridge720 and access router 722) functions as a simple repeater in the samemanner as a cellular repeater. In some embodiments as shown in diagram700A, the wireless bridge may be configured in a point-to-pointconfiguration with a combination of one point-to-point bridge 720 pertrain and at least one access router 722 per railcar 712. Data packetsmay be exchanged between a stationary wireless access point and thepoint-to-point bridge 720 on the train through stationary traveling-waveantenna 716 and onboard traveling-wave antenna 714 enabling wirelessterminals on the train to communicate with stationary wireless networks.

Diagram 700B illustrates a point-to-multipoint configuration, whichpermits each rail car to support a separate sub-network whilecommunicating with the same terrestrial access point via theDoppler-nulling antenna relays. In this configuration, a wireless clientbridge may comprise a plurality of point-to-multipoint routers 718(e.g., one per railcar 712) that may be set to the same service setidentifier. The routers are each connected to a traveling-wavedirectional antenna 714 on the railcar 712 serviced by the router.

FIG. 8 illustrates a general purpose computing device, which may be usedfor software control of wireless communications through atravelling-wave directional antenna in lieu of the hardwareimplementations of FIG's 6 and 7 in accordance with at least someembodiments described herein. In a very basic configuration 802,computing device 800 typically includes one or more processors 804 and asystem memory 806. A memory bus 808 may he used for communicatingbetween processor 804 and system memory 806.

Depending on the desired configuration, processor 804 may be of any typeincluding but not limited to a microprocessor (μP), a microcontroller(μC), a digital signal processor (DSP), or any combination thereof.Processor 804 may include one more levels of caching, such as a cachememory 812, a processor core 814, and registers 816. Example processorcore 814 may include an arithmetic logic unit (ALU), a floating pointunit (FPU), a digital signal processing core (DSP Core), or anycombination thereof. An example memory controller 818 may also be usedwith processor 804, or in some implementations memory controller 815 maybe an internal part of processor 804.

Depending on the desired configuration, system memory 806 may be of anytype including but not limited to volatile memory (such as RAM),non-volatile memory (such as ROM, flash memory, etc.) or any combinationthereof. System memory 806 may include an operating system 820, acommunication application 822, and antenna control module 826. Systemmemory 806 may further include program data 824. Communicationapplication 822 may facilitate wireless communication through an accessnetwork. Antenna control module 826 may control matched traveling wavedirectional antennas mounted to a high-speed rail vehicle and positionedcollinearly alongside the railway such that the antennas continuallytransmit and receive at a fixed angle relative to the motion of thetrain so as to compensate for Doppler shift. The signal transmitted orreceived by the stationary antenna may be conducted to a nearest nodefor communication with an access network. This described basicconfiguration 802 is illustrated in FIG. 8 by those components withinthe inner dashed line.

Computing device 800 may have additional features or functionality, andadditional interfaces to facilitate communications between basicconfiguration 802 and any required devices and interfaces. For example,a bus/interface controller 830 may be used to facilitate communicationsbetween basic configuration 802 and one or more data storage devices 832via a storage interface bus 834. Data storage devices 832 may beremovable storage devices 836, non-removable storage devices 838, or acombination thereof Examples of removable storage and non-removablestorage devices include magnetic disk devices such as flexible diskdrives and bard-disk drives (HDD), optical disk drives such as compactdisk (CD) drives or digital versatile disk (DVD) drives, solid statedrives (SSD), and tape drives to name a few, Example computer storagemedia ma include volatile and nonvolatile, removable and non-removablemedia implemented in any method or technology for storage ofinformation, such as computer readable instructions, data structures,program modules, or other data.

System memory 806, removable storage devices 836 and non-removablestorage devices 838 are examples of computer storage media. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other mediumwhich may be used to store the desired information and which may beaccessed by computing device 800. Any such computer storage media may bepart of computing device 800.

Computing device 800 may also include an interface bus 840 forfacilitating communication from various interface devices (e.g., outputdevices 842, peripheral interfaces 844, and communication devices 866)to basic configuration 802 via bus/interface controller 830. Exampleoutput devices 842 include a graphics processing unit 848 and an audioprocessing unit 850, which may be configured to communicate to variousexternal devices such as a display or speakers via one or more A/V ports852. Example peripheral interfaces 844 include a serial interfacecontroller 854 or a parallel interface controller 856, which may beconfigured to communicate with external devices such as input devices(e.g., keyboard, mouse, pen, voice input device, touch input device,etc.) or other peripheral devices (e.g., printer, scanner, etc.) via oneor more I/O ports 858. An example communication device 866 includes anetwork controller 860, which may be arranged to facilitatecommunications with one or more other computing devices 862 over anetwork communication link via one or more communication ports 864.

The network communication link may be one example of a communicationmedia. Communication media may typically be embodied by computerreadable instructions, data structures, program modules, or other datain a modulated data signal, such as a carrier wave or other transportmechanism, and may include any information delivery media. A “modulateddata signal” may be a signal that has one or more of its characteristicsset or changed in such a manner as to encode information in the signal.By way of example, and not limitation, communication media may includewired media such as a wired network or direct-wired connection, andwireless media such as acoustic, radio frequency (RF), microwave,infrared (IR) and other wireless media. The term computer readable mediaas used herein may include both storage media and communication media.

Computing device 800 may be implemented as a portion of a physicalserver, virtual server, a computing cloud, or a hybrid device thatinclude any of the above functions. Computing device 800 may also beimplemented as a personal computer including both laptop computer andnon-laptop computer configurations. Moreover computing device 800 may beimplemented as a networked system or as part of a general purpose orspecialized server.

Networks for a networked system including computing device 800 maycomprise any topology of servers, clients, switches, routers, modems,Internet service providers, and any appropriate communication media(e.g., wired or wireless communications). A system according toembodiments may have a static or dynamic network topology. The networksmay include a secure network such as an enterprise network (e.g., a LAN,WAN, or WLAN), an unsecure network such as a wireless open network(e.g., IEEE 802.11 wireless networks), or a world-wide network such(e.g., the Internet). The networks may also comprise a plurality ofdistinct networks that are adapted to operate together. Such networksare configured to provide communication between the nodes describedherein. By way of example, and not limitation, these networks mayinclude wireless media such as acoustic, RF, infrared and other wirelessmedia. Furthermore, the networks may be portions of the same network orseparate networks.

Example embodiments may also include methods. These methods can beimplemented in any number of ways, including the structures describedherein. One such way is by machine operations, of devices of the typedescribed in the present disclosure. Another optional way is for one ormore of the individual operations of the methods to be performed inconjunction with one or more human operators performing some of theoperations while other operations are performed by machines. These humanoperators need not be collocated with each other, but each can be onlywith a machine that performs a portion of the program. In otherexamples, the human interaction can be automated such as by pre-selectedcriteria that are machine automated.

FIG. 9 is a flow diagram illustrating an example method for use oftravelling-wave directional antenna in high-speed vehicle wirelesscommunications that may be performed in a computing device such asdevice 800 in FIG. 8 in accordance with at least some embodimentsdescribed herein. The operations described in FIG. 9 may be performed asa result of execution of instructions stored in a computer-readablemedium 920 by controller device 910. Controller device 910 may be aspecial purpose control device or a general purpose computer such ascomputing device 800 of FIG. 8.

An example process according to embodiments may begin with operation922, “AGGREGATE WIRELESS TRAFFIC ON MOVING VEHICLE”, where wirelesscommunications to and from mobile devices on a moving vehicle (e.g., ahigh-speed train car) may be aggregated at a wireless node (e.g., arouter) 232 or a train access terminal 248. Operation 922 may befollowed by operation 924, “TRANSMIT SIGNALS TO A STATIONARYTRAVELING-WAVE ANTENNA THROUGH A TRAVELING-WAVE ANTENNA ON THE MOVINGVEHICLE”, where the train access terminal 248 may cause the aggregatedtraffic to be facilitated through continual transmission by the leakycoax antenna 245 to a stationary leaky coax traveling-wave antenna 226along the railway at a fixed angle relative to the motion of the trainso as to compensate for Doppler shift.

Operation 924 may be followed by optional operation 926, “CONDUCTRECEIVED SIGNALS TO AN ACCESS NODE BEHIND THE MOVING VEHICLE”, wheresignals may be forwarded from the stationary leaky coax traveling-waveantenna 226 along the railway to the access network (222) through one ofa plurality of access nodes. Optional operation 926 may be followed byoperation 928, “RECEIVE SIGNALS FROM A STATIONARY TRAVELING-WAVE ANTENNATHROUGH A TRAVELING-WAVE ANTENNA ON THE MOVING VEHICLE”, where the trainaccess terminal 248 may receive signals from the access network (224)through the leaky coax antenna 245 through transmission at a fixed anglerelative to the motion of the train. Operation 928 may be followed byoptional operation 930, “CONDUCT TRANSMITTED SIGNALS TO AN ACCESS NODEIN FRONT OF THE MOVING VEHICLE”, where signals may be forwarded from thestationary leaky coax traveling-wave antenna 226 along the railway tothe access network (222) through one of a plurality of access nodes.

FIG. 10 is a flow diagram illustrating an example method for use oftraveling-wave directional antenna in high-speed vehicle communicationsthat may be performed in a cellular repeating device such as 620 in FIG.6 in accordance with at least some embodiments described herein. Theoperations described in FIG. 10 may be performed as a result ofexecution of instructions stored in a computer-readable medium 1020 bycontroller device 1010.

An example process according to embodiments may begin with operation1022, “RECEIVE ONBOARD CELLULAR SIGNALS”, where cellular signals fromcellular phones on moving vehicle 612 may be received using and onboardreceive (non-directional) antenna 624. Operation 1022 may be followed byoperation 1024, “AMPLIFY RECEIVED SIGNALS”, where the received signalsmay be amplified at the onboard cellular repeater 620 for transmissionbetween relay antennas.

Operation 1024 may be followed by operation 1026, “RELAY SIGNALS TOSTATIONARY TRAVELING-WAVE ANTENNA”, where the amplified cellular signalsmay be relayed from traveling-wave antenna on the moving vehicle 612 tostationary traveling-wave antenna 226. The signals may be launched fromthe back/front of the vehicle toward the front/back of the vehicle,respectively.

Operation 1026 may be followed by operation 1028, “CONDUCT SIGNALS TOCELLULAR BASE STATION”, where the relayed signals may be received on thestationary traveling-wave antenna and conducted to a cellular basestation in-front-of/behind the vehicle. The received signals may beconducted in a direction toward/opposite the direction of motion of thevehicle, respectively.

Operation 1028 may be followed by operation 1030, “RECEIVE SIGNALS ATSTATIONARY TRAVELING-WAVE ANTENNA FROM CELLULAR BASE STATION”, wherereturn signals from the cellular base station located behind/in-front ofthe vehicle may be relayed along the stationary traveling-wave antennain the direction toward/opposite the motion of the vehicle,respectively.

Operation 1030 may be followed by operation 1032, “RELAY CELLULARSIGNALS FROM STATIONARY TRAVELING-WAVE ANTENNA TO ONBOARD TRAVELING-WAVEANTENNA”, where the cellular signals may be relayed from the stationarytraveling-wave antenna to the traveling-wave antenna on the movingvehicle. The signals launched from the base station behind/in-front-ofthe vehicle may be received at the front/back of the vehicle,respectively.

Operation 1032 may be followed by operation 1034, “AMPLIFY RELAYEDSIGNALS AT CELLULAR REPEATER”, where the signals may be relayed fromrelay antennas to the non-directional antenna(s) at the cellularrepeater 620.

Operation 1034 may be followed by operation 1036, “TRANSMIT SIGNALS TOONBOARD CELLULAR PHONES”, where the cellular signals received from thebase station are transmitted from the onboard transmit antenna tocellular phones in the moving vehicle.

FIG. 11 is a flow diagram illustrating an example method for use oftraveling-wave directional antenna in high-speed vehicle communicationsthat may be performed in a client bridge device such as 718 in FIG. 7 inaccordance with at least some embodiments described herein. Theoperations described in FIG. 11 may be performed as a result ofexecution of instructions stored in a computer-readable medium 1120 bycontroller device 1110.

An example process according to embodiments may begin with operation1122, “RECEIVE ONBOARD WIRELESS PACKET DATA”, where packet data trafficfrom wireless data terminals on moving vehicle 712 may be received usingonboard point-to-multipoint router 718 or access router 722. Operation1122 may be followed by operation 1124, “AGGREGATE & BUFFER PACKETDATA”, where the data packets received from terminals at the data-linklayer may be aggregated and buffered using point-to-multipoint router718 according to a point-to-multipoint protocol (e.g., WirelessDistribution System or access point-client configuration) orpoint-to-point bridge 720.

Operation 1124 may be followed by operation 1126, “RELAY DATA TRAFFIC TOSTATIONARY TRAVELING-WAVE ANTENNA”, where the data traffic from thetraveling-wave antenna 714 on moving vehicle 712 may be relayed to thestationary traveling-wave antenna 716. The signals may be launched fromthe back/front of the vehicle toward the front/back of the vehicle,respectively.

Operation 1126 may be followed by operation 1128, “CONDUCT DATA TRAFFICTO ACCESS POINT”, where the relayed data traffic may be received on thestationary traveling-wave antenna 716 and conducted to a wireless accesspoint in-front-of/behind the vehicle. The received traffic may beconducted in a direction toward/opposite the direction of motion of thevehicle, respectively.

Operation 1128 may be followed by operation 1130, “RECEIVE DATA TRAFFICAT STATIONARY TRAVELING-WAVE ANTENNA FROM ACCESS POINT”, where returnpacket data traffic may be conducted from the wireless access pointlocated behind/in-front of the vehicle along stationary traveling-waveantenna 716 in the direction toward/opposite the motion of the vehicle,respectively.

Operation 1130 may be followed by operation 1132, “RELAY DATA TRAFFICFROM STATIONARY TRAVELING-WAVE ANTENNA TO ONBOARD TRAVELING- WAVEANTENNA”, where the data traffic from the stationary traveling-waveantenna 716 may be relayed to the traveling-wave antenna 714 on themoving vehicle 712. The signals launched from the base stationbehind/in-front-of the vehicle may be received at the front/back of thevehicle, respectively.

Operation 1132 may be followed by operation 1134, “AGGREGATE & BUFFERDATA PACKETS AT ONBOARD WIRELESS BRIDGE”, where the data packetsreceived from the wireless access point at the data-link layer may beaggregated and buffered using point-to-multipoint router 718 accordingto a point-to-multipoint protocol (e.g., Wireless Distribution System oraccess point-client configuration) or point-to-point bridge 720.

Operation 1134 may be followed by operation 1136, “TRANSMIT DATA PACKETSTO ONBOARD WIRELESS DEVICES”, where the packet data traffic receivedfrom wireless access point is transmitted to wireless devices in themoving vehicle 712 using the onboard transmit antenna system.

The operations included in the processes of FIGS. 9, 10, and 11described above are for illustration purposes. Using a travelling-wavedirectional antenna in high-speed vehicle wireless communications may beimplemented by similar processes with fewer or additional operations. Insome examples, the operations may be performed in a different order. Insome other examples, various operations may be eliminated. In stillother examples, various operations may be divided into additionaloperations, or combined together into fewer operations. Althoughillustrated as sequentially ordered operations, in some implementationsthe various operations may be performed in a different order, or in somecases various operations may be performed at substantially the sametime.

FIG. 12 illustrates a block diagram of an example computer programproduct, arranged in accordance with at least some embodiments describedherein.

In some examples, as shown in FIG. 12, computer program product 1200 mayinclude a signal bearing medium 1202 that may also include machinereadable instructions 1204 that, when executed by, for example, aprocessor, may provide the functionality described above with respect toFIG. 2 through FIG. 5. Thus, for example, referring to processor 804,one or more of the tasks shown in FIG. 12 may be undertaken in responseto instructions 1204 conveyed to the processor 804 by signal bearingmedium 1202 to perform actions associated with eliminating Doppler shiftin high-speed wireless communications as described herein. Some of thoseinstructions may include aggregating wireless traffic on board a movingvehicle and enabling communication with a terrestrial network through amatched pair of traveling-wave directional antennas.

In some implementations, signal bearing medium 1202 depicted in FIG. 12may encompass a computer-readable medium 1206, such as, but not limitedto, a hard disk drive, a Compact Disc (CD), a Digital Versatile Disk(DVD), a digital tape, memory, etc. In some implementations, signalbearing medium 1202 may encompass a recordable medium 1208, such as, butnot limited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In someimplementations, signal bearing medium 1202 may encompass acommunications medium 1210, such as, but not limited to, a digitaland/or an analog communication medium (e.g., a fiber optic cable, awaveguide, a wired communications link, a wireless communication link,etc.). Thus, for example, computer program product 1200 may be conveyedto the processor 804 by an RF signal bearing medium 1202, where thesignal bearing medium 1202 is conveyed by a wireless communicationsmedium 1210 (e.g., a wireless communications medium conforming with theIEEE 802.11 standard).

According to some examples, a method for enhancing wirelesscommunications in high-speed vehicles through Doppler-nullingtraveling-wave antenna relays may include aggregating wireless trafficfrom a plurality of wireless communication devices at an access terminalon a moving vehicle; and forwarding the wireless traffic to a wirelesscommunication network through a pair of matched traveling-wavedirectional antennas. A first of the antennas may be positioned on themoving vehicle and a second of the antennas may be positioned along apath of the moving vehicle. The second antenna may be conductivelycoupled to one or more access nodes of the wireless communicationnetwork.

The first and second antennas may be suitably designed to radiatecontinuously along their length in highly directional beams and arrangedto transmit and receive at a predefined angle relative to a motion ofthe moving vehicle. The predefined angle may deviate from 90 degreesbetween about 5 degrees and about 10 degrees. In some examples, thepredefined angle may be selected to correspond to a Doppler null.

The method may also include conducting signals received at the secondantenna to a nearest access node of the wireless communication network,conducting signals received from the moving vehicle to an access nodebehind the moving vehicle, and/or conducting signals transmitted to themoving vehicle to an access node in front of the moving vehicle. Themoving vehicle may be a high-speed train with the first antenna affixedto a train car and the second antenna positioned along a railroad.

The first and/or the second antenna may be a leaky coaxial cableantenna, a slot array antenna, a directional dipole array antenna,and/or a patch array antenna. The method may further include positioninga first array of radiating elements of the first and second antennas ata periodic predefined distance such that a guided wave mode of theantennas couples into a single radiation mode. A second array ofradiating elements may be interleaved along each antenna offset by abouta quarter of the periodic predefined distance from the first array ofradiating elements such that a stop band in the guided wave mode atwavelengths that couple into a broadside radiation mode is eliminated.

According to other examples, a wireless communication system enablingcommunication between high-speed vehicles and a terrestrial networkthrough Doppler-nulling traveling-wave antenna relays may include anaccess terminal adapted to aggregate wireless traffic from a pluralityof wireless communication devices on a moving vehicle and forward theaggregated wireless traffic to the terrestrial network through a pair ofmatched traveling-wave directional antennas, a first traveling-wavedirectional antenna affixed to the moving vehicle, and a secondtraveling-wave directional antenna positioned along a path of the movingvehicle. The second antenna may be conductively coupled to one or moreaccess nodes of the wireless communication network.

The first and second antennas may be suitably designed to radiatecontinuously along their length in highly directional beams and arrangedto transmit and receive at a predefined angle relative to a motion ofthe moving vehicle. The predefined angle may deviate from 90 degreesbetween about 5 degrees and about 10 degrees. In some examples, thepredefined angle may be selected to correspond to a Doppler null.

Signals received at the second antenna may be conducted to a nearestaccess node of the terrestrial network. Signals received from the movingvehicle may be conducted to an access node behind the moving vehicle.Signals transmitted to the moving vehicle may be conducted to an accessnode in front of the moving vehicle. Furthermore, the moving vehicle maybe a high-speed train, the first antenna affixed to a train car, and thesecond antenna positioned along a railroad.

The first and/or the second antenna may be a leaky coaxial cableantenna, a slot array antenna, a directional dipole array antenna,and/or a patch array antenna. A first array of radiating elements of thefirst and second antennas may be positioned at a periodic predefineddistance such that a guided wave mode of the antennas couples into asingle radiation mode. A second array of radiating elements may beinterleaved along each antenna offset by about a quarter of the periodicpredefined distance from the first array of radiating elements such thata stop band in the guided wave mode at wavelengths that couple into abroadside radiation mode is eliminated.

According to further examples, a traveling-wave, directional antennasystem for enabling wireless communication between high-speed vehiclesand a terrestrial network may include a first traveling-wave directionalantenna affixed to a moving vehicle adapted to receive aggregatedwireless traffic from a plurality of wireless communication devices onthe moving vehicle and forward the wireless traffic to the terrestrialnetwork through a matching second traveling-wave antenna and the secondtraveling-wave directional antenna positioned along a path of the movingvehicle and conductively coupled to one or more access nodes of thewireless communication network.

The first and second antennas may be suitably designed to radiatecontinuously along their length in highly directional beams and arrangedto transmit and receive at a predefined angle relative to a motion ofthe moving vehicle. The predefined angle may deviate from 90 degreesbetween about 5 degrees and about 10 degrees. In some examples, thepredefined angle may be selected to correspond to a Doppler null.

The second antenna may be adapted to conduct signals received from thefirst antenna to a nearest access node of the terrestrial network. Thesecond antenna may further be adapted to conduct signals received fromthe moving vehicle to an access node behind the moving vehicle. Thesecond antenna may also be adapted to conduct signals transmitted to themoving vehicle to an access node in front of the moving vehicle.

The moving vehicle may be a high-speed train with the first antennaaffixed to a train car and the second antenna positioned along arailroad. The first and/or second antenna may be a leaky coaxial cableantenna, a slot array antenna, a directional dipole array antenna,and/or a patch array antenna. A first array of radiating elements of thefirst and second antennas may be positioned at a periodic predefineddistance such that a guided wave mode of the antennas couples into asingle radiation mode. A second array of radiating elements may beinterleaved along each antenna offset by about a quarter of the periodicpredefined distance from the first array of radiating elements such thata stop band in the guided wave mode at wavelengths that couple into abroadside radiation mode is eliminated.

There is little distinction left between hardware and softwareimplementations of aspects of systems; the use of hardware or softwareis generally (but not always, in that in certain contexts the choicebetween hardware and software may become significant) a design choicerepresenting cost vs. efficiency tradeoffs. There are various vehiclesby which processes and/or systems and/or other technologies describedherein may be effected (e.g., hardware, software, and/or firmware), andthat the preferred vehicle will vary with the context in which theprocesses and/or systems and/or other technologies are deployed. Forexample, if an implementer determines that speed and accuracy areparamount, the implementer may opt for a mainly hardware and/or firmwarevehicle; if flexibility is paramount, the implementer may opt for amainly software implementation; or, yet again alternatively, theimplementer may opt for some combination of hardware, software, and/orfirmware.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples. Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/for operations, it will beunderstood h those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples may be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof In one embodiment,several portions of the subject matter described herein may beimplemented via Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), digital signal processors (DSPs), orother integrated formats. However, those skilled in the art willrecognize that some aspects of the embodiments disclosed herein, inwhole or in part, may be equivalently implemented in integratedcircuits, as one or more computer programs running on one or morecomputers e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g. as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and/or firmwarewould be well within the skill of one of skill in the art in light ofthis disclosure.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, reagents, compounds compositions or biological systems, whichcan, of course, vary. It is also to be understood that the terminologyused herein is for the purpose of describing particular embodimentsonly, and is not intended to be limiting.

In addition, those skilled in the art will appreciate that themechanisms of the subject matter described herein are capable of beingdistributed as a program product in a variety of forms, and that anillustrative embodiment of the subject matter described herein appliesregardless of the particular type of signal bearing medium used toactually carry out the distribution. Examples of a signal bearing mediuminclude, but are not limited to, the following: a recordable type mediumsuch as a floppy disk, a hard disk drive, a Compact Disc (CD), a DigitalVersatile Disk (DVD), a digital tape, a computer memory, etc.; and atransmission type medium such as a digital and/or an analogcommunication medium (e.g., a fiber optic cable, a waveguide, a wiredcommunications link, a wireless communication link, etc.).

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use engineering practices to integrate such describeddevices and/or processes into data processing systems. That is, at leasta portion of the devices and/or processes described herein may beintegrated into a data processing system via a reasonable amount ofexperimentation. Those having skill in the art will recognize that atypical data processing system generally includes one or more of asystem unit housing, a video display device, a memory such as volatileand non-volatile memory, processors such as microprocessors and digitalsignal processors, computational entities such as operating systems,drivers, graphical user interfaces, and applications programs, one ormore interaction devices, such as a touch pad or screen, and/or controlsystems including feedback loops and control motors (e.g., feedback forsensing position and/or velocity of gantry systems; control motors formoving and/or adjusting components and/or quantities).

A typical data processing system may be implemented utilizing anysuitable commercially available components, such as those typicallyfound in data computing/communication and/or networkcomputing/communication systems. The herein described subject mattersometimes illustrates different components contained within, orconnected with, different other components. It is to be understood thatsuch depicted architectures are merely exemplary, and that in fact manyother architectures may be implemented which achieve the samefunctionality. In a conceptual sense, any arrangement of components toachieve the same functionality is effectively “associated” such that thedesired functionality is achieved. Hence, any two components hereincombined to achieve a particular functionality may be seen as“associated with” each other such that the desired functionality isachieved, irrespective of architectures or intermediate components.Likewise, any two components so associated may also be viewed as being“operably connected”, or “operably coupled”, to each other to achievethe desired functionality, and any two components capable of being soassociated may also be viewed as being “operably couplable”, to eachother to achieve the desired functionality. Specific examples ofoperably couplable include but are not limited to physically connectableand/or physically interacting components and/or wirelessly interactableand/or wirelessly interacting components and/or logically interactingand/or logically interactable components.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations).

Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember. Thus, for example, a group having 1-3 cells refers to groupshaving 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers togroups having 1, 2, 3, 4, or 5 cells, and so forth.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A system to enhance wireless communications inhigh-speed vehicles through Doppler-nulling traveling-wave antennarelays, the system comprising; an access terminal on a vehicle adaptedto transmit wireless communication signals to and receive wirelesscommunication signals from a wireless communication network through apair of leaky traveling-wave antennas; and the pair of leakytraveling-wave antennas arranged to radiate substantiallyperpendicularly to a direction of motion of the vehicle, wherein a firstof the leaky traveling-wave antennas is positioned on the vehicle; asecond of the leaky traveling-wave antennas is positioned along a pathof the vehicle and is conductively coupled to one or more access nodesof the wireless communication network; and a Doppler frequency shift onthe transmitted communication signals and the received communicationsignals resulting from a motion of the first leaky traveling-waveantenna relative to the second leaky traveling-wave antenna is minimizedto zero due to the substantially perpendicular radiation of the pair ofleaky traveling wave antennas relative to the direction of motion of thevehicle.
 2. The system of claim 1, wherein the second leakytraveling-wave antenna conducts the transmitted communication signalsand the received communication signals to a nearest access node of thewireless communication network.
 3. The system of claim 2, wherein thetransmitted communication signals are conducted to an access node behindthe vehicle.
 4. The system of claim 2, wherein the receivedcommunication signals are conducted to an access node in front of thevehicle.
 5. The system of claim 1, wherein a first array of radiatingelements of the first and second leaky traveling-wave antennas arepositioned at a periodic predefined distance such that a guided wavemode of the first and second leaky traveling-wave antennas couples intoa single radiation mode.
 6. The system of claim 5, wherein a secondarray of radiating elements are interleaved along the first and secondleaky traveling-wave antennas offset by about a quarter of the periodicpredefined distance from the first array of radiating elements such thata stop band in the guided wave mode at wavelengths that couple into abroadside radiation mode is eliminated.
 7. A vehicle capable ofcommunication with a terrestrial network through Doppler-nullingtraveling-wave antenna relays, the vehicle comprising: an accessterminal: and a first leaky traveling-wave antenna adapted to transmitwireless communication signals from the access terminal to theterrestrial network through a second leaky traveling-wave antenna,wherein the second leaky traveling-wave antenna is positioned along apath of the vehicle and is conductively coupled to one or more accessnodes of the terrestrial network; and the first and second leakytraveling-wave antennas are arranged to radiate substantiallypetpendicularly to a direction of motion of the vehicle such that aDoppler frequency shift on the transmitted communication signalsresulting from a motion of the first leaky traveling-wave antennarelative to the second leaky traveling-wave antenna is minimized tozero.
 8. The vehicle of claim 7, wherein the first leaky traveling-waveantenna is further adapted to provide the access terminal with wirelesscommunication signals received from the terrestrial network through thesecond leaky traveling-wave antenna.
 9. The vehicle of claim 7, whereinthe first leaky traveling-wave antenna is suitably designed to radiatecontinuously along its length in highly directional beams.
 10. Thevehicle of claim 7, wherein the first leaky traveling-wave antenna isfurther adapted to transmit the wireless communication signals at apredefined angle.
 11. The vehicle of claim 10, wherein the predefinedangle deviates from 90 degrees between about 5 degrees and about 10degrees.
 12. The vehicle of claim 7, wherein a length of the first leakytraveling-wave antenna is substantially equal to a length of thevehicle.
 13. the vehicle of claim 7, wherein the first leakytraveling-wave antenna is one of a leaky coaxial cable antenna, a slotarray antenna, a directional dipole array antenna, and a patch arrayantenna.
 14. A traveling-wave antenna system to enable wirelesscommunication between high-speed vehicles and a terrestrial network, thesystem comprising: a moving, antenna affixed to a vehicle and adapted totransmit wireless communication signals from an access terminal on thevehicle to the terrestrial network through a stationary antenna; and thestationary antenna positioned, along, a path of the vehicle andconductively coupled to one or more access nodes of the terrestrialnetwork, wherein the moving antenna and the stationary antenna arearranged to radiate substantially perpendicularly to a direction ofmotion of the vehicle such that a Doppler frequency shift on thetransmitted communication signals resulting from a motion of the movingantenna relative to the stationary antenna is minimized to zero.
 15. Theantenna system of claim 14, wherein the moving antenna and thestationary antenna are leaky coaxial cables.
 16. The antenna system ofclaim 15, wherein a first array of radiating elements in an outerconductor sheath of the leaky coaxial cables are positioned at aperiodic predefined distance such that a guided wave mode of the leakycoaxial cables couples into a single radiation mode.
 17. The antennasystem of claim 16, wherein a radiation angle of the single radiationmode is given by θ⁻¹=sin⁻¹(√{square root over (ε)}−λ/P), wherein ε is adielectric constant of a spacer material between the first array ofradiating elements, λ is a free space wavelength of a radiated wave fromthe leaky coaxial cables, and P is the periodic predefined distancebetween the first array of radiating elements of the leaky coaxialcables.
 18. The antenna system of claim 16, wherein a second array ofradiating, elements in the outer conductor sheath of the leaky coaxialcables are positioned along each leaky coaxial cable offset by about aquarter of the periodic predefined distance from the first array ofradiating elements such that a stop band in the guided wave mode atwavelengths that couple into a broadside radiation mode is eliminated.19. The antenna system of claim 14, wherein the moving antenna isfurther adapted to provide the access terminal with wirelesscommunication signals received from the terrestrial network through thestationary antenna.
 20. The antenna system of claim 19, wherein thestationary antenna is adapted to conduct the transmitted communicationsignals and the received wireless communication signals to a nearestaccess node of the terrestrial network.